Autofocus system

ABSTRACT

An autofocus system includes: an imaging unit which captures an image of an object formed by an optical system; an autofocus portion which performs focus adjustment of the optical system on an autofocus area set in the image captured by the imaging unit so that the object within the autofocus area comes into focus; an AF area tracking processing portion which performs tracking processing to set a predetermined object within the autofocus area as a target to be tracked, detect a presence area of the target to be tracked in an image newly captured by the imaging unit and determine the presence area as a new autofocus area; a depth-of-field computing portion which calculates a depth of field based on information acquired from the optical system; and a control portion as defined herein.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of International Application No.PCT/JP2012/050979 filed on Jan. 18, 2012, and claims priority fromJapanese Patent Application No. 2011-008333 filed on Jan. 18, 2011, theentire disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an autofocus system provided with anautomatic tracking function of defining an object within an autofocus(AF) area as an object to be tracked and updating the AF area accordingto the position of the object to be tracked.

BACKGROUND ART

There is known a television camera system for broadcasting use orbusiness use, provided with an autofocus function of automaticallyfocusing on an object within a specific imaging area. This type camerasystem generally uses contrast-method AF which is performed by detectingthe height of contrast of a captured image and controlling the focus ofa capturing optical system to maximize (locally maximize) the contrast.

As to focusing by AF, focusing is generally performed not on the entirescreen of the captured image but on an object within an area (autofocusarea) which is a part of the captured image. That is, in the contrastmethod, focus adjustment is performed to maximize the contrast of thecaptured image (object image) within the autofocus area.

An autofocus system with an automatic tracking function as shown inPatent Literature 1 is known as a system to achieve the autofocusfunction. The autofocus system in Patent Literature 1 uses an AF mode inwhich either of a fixation mode to turn off the automatic trackingfunction and a tracking mode to turn on the automatic tracking functionis selected by an operation of a user.

CITATION LIST

Patent Literature

-   Patent Literature 1: Japanese Patent No. 4418344

SUMMARY OF INVENTION Problem to be Solved by the Invention

Incidentally, in the autofocus system with the automatic trackingfunction, mistracking is apt to occur when the angle of view is changedto a wide angle side by zooming in a state where automatic tracking isperformed. When the angle of view is then changed from the wide angleside to a telephoto side, there is a possibility that another objectthan the intended object will be tracked.

Moreover, even if an object within an autofocus area is in focus, thereis a possibility that the object will be out of focus when the angle ofview is then changed by zooming.

In the camera in Patent Literature 1, mistracking is apt to occur whenthe angle of view is changed by zooming because the automatic trackingfunction cannot be automatically switched on/off in accordance with thechange in the angle of view by zooming.

The invention provides an autofocus system provided with an automatictracking function, in which occurrence of mistracking can be suppressedwhen the angle of view is changed by zooming.

Means for Solving the Problem

An autofocus system according to the invention includes:

an imaging unit which captures an image of an object formed by anoptical system;

an autofocus portion which performs focus adjustment of the opticalsystem on an autofocus area set in the image captured by the imagingunit so that the object within the autofocus area comes into focus;

an AF area tracking processing portion which performs trackingprocessing to set a predetermined object within the autofocus area as atarget to be tracked, detect a presence area of the target to be trackedin an image newly captured by the imaging unit and determine thepresence area as a new autofocus area;

a depth-of-field computing portion which calculates a depth of fieldbased on information acquired from the optical system; and

a control portion which controls execution of the focus adjustment bythe autofocus portion and the tracking processing by the AF areatracking processing portion based on the depth of field calculated bythe depth-of-field computing portion.

Advantageous Effects of Invention

According to the invention, it is possible to provide an autofocussystem provided with an automatic tracking function, in which occurrenceof mistracking can be suppressed when the angle of view is changed byzooming.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A block diagram showing an overall configuration of a videocamera system for explaining an autofocus system according to anembodiment of the invention.

FIG. 2 A view for explaining an example of an autofocus area in theautofocus system according to the embodiment of the invention.

FIG. 3 A view showing an example of a screen displayed on a touchpanel-including liquid crystal display in the video camera system inFIG. 1.

FIG. 4 A view showing an example of the screen displayed on the LCD whenautomatic tracking is stopped.

FIG. 5 A flowchart showing a processing procedure in an automatictracking mode in the autofocus system according to the embodiment of theinvention.

FIG. 6 A flow chart showing a processing procedure of autofocusadjustment control in the autofocus system according to the embodimentof the invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

An embodiment of an autofocus system with an automatic tracking functionaccording to the invention will be described below with reference to thedrawings.

FIG. 1 is a block diagram showing an overall configuration of a videocamera system for explaining the autofocus system according to theembodiment of the invention. For example, this video camera system isused for capturing an image with a television camera for broadcastinguse or business use.

As shown in FIG. 1, the video camera system 1 includes a televisioncamera 10, an image processing unit 18 constituting an AF area trackingprocessing portion performing automatic tracking, and an AF frameoperation portion 20.

The television camera 10 includes a camera body 14 made of an HD cameracorresponding to a high-definition television (HD TV) system, and a lensdevice 12 having an imaging lens (optical system) attached to a lensmount of the camera body 14.

An image sensing device (for example, a CCD image sensing device), arequired signal processing circuit, etc. are mounted in the camera body14. An image formed by the imaging lens of the lens device 12 isphotoelectrically converted by the image sensing device and thensubjected to required signal processing by the signal processingcircuit, so that the image is outputted as an HDTV-system video signal(HDTV signal) to the outside from a video signal output terminal, etc.of the camera body 14.

A viewfinder 16 is further mounted in the camera body 14 so that eachimage captured by the television camera 10 is displayed on theviewfinder 16. Various kinds of information other than the capturedimage is further displayed on the viewfinder 16. For example, an image(frame image) indicating an AF frame which is the contour of thecurrently set autofocus area is displayed while superimposed on thecaptured image.

The lens device 12 has an imaging lens (zoom lens) attached to the lensmount of the camera body 14 so that an image of an object 28 is formedon an imaging surface of an image sensing device of the camera body 14by the imaging lens. Though not shown, movable portions for adjustingimaging conditions such as a focus lens group, a zoom lens group, adiaphragm, etc. are provided as constituent elements of the imaginglens. These movable portions are electrically driven by a motor (servomechanism). For example, the focus lens group and the zoom lens groupmove in an optical axis direction so that the focus (object distance) isadjusted by the movement of the focus lens group while the focaldistance (zoom ratio) is adjusted by the movement of the zoom lensgroup.

Incidentally, as long as at least the focus lens group can beelectrically driven, the other movable portions may be driven onlymanually in the system concerned with autofocus adjustment.

An AF unit 40 and a lens CPU not shown, etc. are further mounted in thelens device 12. The lens CPU generally controls the lens device 12 as awhole. The AF unit 40 is a processing portion for acquiring informationnecessary for focus control (automatic focus adjustment) based on theautofocus adjustment. Though not shown, an AF processing portion, an AFimaging circuit, etc. constitute the AF unit 40.

The AF imaging circuit is disposed in the lens device 12 in order toacquire a video signal for AF processing. The AF imaging circuit has animage sensing device (referred to as AF image sensing device) such as aCCD image sensing device, and a processing circuit which outputs anoutput signal of the AF image sensing device as a video signal with apredetermined format. Incidentally, the video signal outputted from theAF imaging circuit is a luminance signal.

Object light incident on the image sensing device of the camera body 14is branched by a half mirror or the like disposed on an optical path ofthe imaging lens, so that an image of the branched object light isformed on the imaging surface of the AF image sensing device. Theimaging area and the object distance (the distance to the object cominginto focus) in the AF image sensing device are formed to be coincidentwith the imaging area and the object distance in the image sensingdevice of the camera body 14, so that the object image taken in by theAF image sensing device is coincident with the object image taken in bythe image sensing device of the camera body 14. Incidentally, theimaging ranges of the two image sensing devices do not need to beperfectly coincident with each other. For example, the imaging range ofthe AF image sensing device may be a larger range including the imagingrange of the image sensing device of the camera body 14.

The AF processing portion acquires a video signal from the AF imagingcircuit, and calculates a focus evaluation value indicating the level ofcontrast of an object image within the autofocus area based on the videosignal. For example, after a high frequency component signal isextracted by a high pass filter from the video signal obtained from theAF image sensing device, a signal of an image of the autofocus area setas will be described later, among the high frequency component signal,is integrated scene by scene (frame by frame). The integrated valueobtained thus scene by scene indicates the level of contrast of theimage of the autofocus area. The integrated value is given as a focusevaluation value to the lens CPU.

The lens CPU acquires information of an AF frame (AF frame information)indicating contour information (position, size, shape etc.) of theautofocus area from the image processing unit 18 as will be describedlater, and designates the autofocus area designated by the AF frameinformation as a target range for AF processing. The focus evaluationvalue obtained based on the image (video signal) of the autofocus areais acquired from the AF processing portion.

Whenever the video signal for one scene is acquired thus from the AFimaging circuit (whenever a focus evaluation value is obtained by the AFprocessing portion), the focus evaluation value is acquired from the AFprocessing portion and the focus lens group is controlled to maximize(locally maximize) the acquired focus evaluation value, that is, tomaximize the contrast of the object image within the autofocus area. Forexample, a mountain-climbing method is generally known as the focus lensgroup controlling method based on the focus evaluation value. The focuslens group is moved in a direction of increasing the focus evaluationvalue. When a point at which the focus evaluation value begins todecrease is detected, the focus lens group is set at that position. Inthis manner, the object within the autofocus area is brought into focusautomatically.

Although the aforementioned AF processing portion acquires a videosignal from the AF image sensing device mounted in the lens device 12 inorder to calculate the focus evaluation value, configuration may be madeso that the aforementioned AF processing portion acquires a video signalof each image captured by the image sensing device of the camera body 14from the camera body 14. In addition, any AF unit may be used as long asthe AF unit can automatically focus on an object within the autofocusarea.

Next, the autofocus area in the autofocus system according to theembodiment of the invention will be described. FIG. 2 is a view showingan example of the autofocus area in the autofocus system according tothe embodiment of the invention. As shown in FIG. 2, an autofocus area200 is set as a quadrilateral area with respect to an imaging area 202(or an imaging range) of the image sensing device in the camera body 14.The contour of the autofocus area 200 is indicated as an AF frame 204.In the autofocus system according to the embodiment of the invention, anobject to be imaged within the autofocus area 200 (area within the AFframe 204) of the image sensing device is brought into focus.

Incidentally, this specification is placed on the assumption that theautofocus area 200 relative to the imaging area 202 is determined basedon three factors, i.e. the position, size and shape (aspect ratio) ofthe contour (AF frame 204) of the autofocus area 200 and the autofocusarea 200 is changed when at least one of the three factors, i.e. theposition, size and shape of the AF frame 204 is changed.

In addition, the lens device 12 is connected to the camera body 14through a cable or directly so that various information can be exchangedbetween the lens device 12 and the camera body 14 through serialcommunication interfaces 12 a and 14 a provided respectively in the lensdevice 12 and the camera body 14. In this manner, information of the AFframe set currently in the AF unit 40 is also transmitted to the camerabody 14, and an image of the AF frame corresponding to the position,size and shape of the AF frame set currently in each video imagedisplayed on the viewfinder 16 by processing in the camera body 14 isdisplayed while superimposed on the video image.

The image processing unit 18 is a processing portion for designating theautofocus area (the position, size and shape (aspect ratio) of the AFframe) set in the AF unit 40 of the lens device 12 by manual operationor automatic tracking processing which will be described later. Forexample, the image processing unit 18 is received in a not-shown housingand placed in a side portion of a barrel of the imaging lens of the lensdevice 12, an outer wall surface of the housing of the camera body 14etc. Incidentally, the position where the image processing unit 18 isplaced in the lens device 12 or the camera body 14 is not limitedthereto but may be any other arbitrary position. In addition, the imageprocessing portion 18 may be disposed in a portion other than the lensdevice 12 or the camera body 14.

The image processing unit 18 has an SCI 58. The SCI 58 is connected tothe lens device 12 so the SCI 58 can exchange various signals with thelens CPU through the SCI 12 a. In this manner, AF frame information fordesignating the autofocus area 200 is given to the lens CPU of the lensdevice 12 from the image processing unit 18 so that the autofocus area200 in the AF unit 40 is set based on the AF frame information.

In addition, a video input connector for importing a video signal isprovided in the image processing unit 18. A video output connector ofthe camera body 14 is connected to the video input connector through adown converter 46. In this manner, an HDTV signal outputted from thevideo output connector of the camera body 14 is converted(down-converted) into a standard television (NTSC (National TelevisionSystem Committee) type video signal (SDTV signal) and inputted to theimage processing unit 18.

Although details will be given later, the image processing unit 18performs processing for fetching each captured image corresponding toone frame sequentially from the video signal inputted from the camerabody 14 and detecting an object as a predetermined target to be trackedfrom the captured image when automatic tracking processing is executed.The image processing unit 18 determines the autofocus area 200 so as tobring the object into focus by AF, and then transmits information of thedetermined autofocus area 200 to the lens CPU of the lens device 12.Incidentally, the configuration and processing contents of the imageprocessing unit 18 will be described later.

The AF frame operation portion 20 is provided as a device integratedwith the image processing unit 18. A touch panel-including liquidcrystal display (LCD) 66 which will be described later is configured tobe detachable from the image processing unit 18. Incidentally, the AFframe operation portion 20 may be provided in such a form that the AFframe operation portion 20 is partially or entirely formed as a separatedevice from the image processing unit 18 and connected to the imageprocessing unit 18 by a cable etc.

The AF frame operation portion 20 is an operation portion for mainlyperforming operation concerned with control of the AF frame. The AFframe operation portion 20 is provided with an operation member by whichan operator can input an instruction of the autofocus area 200 by manualoperation, and an operation member by which operation concerned withautomatic tracking for automatically tracking a desired object can beperformed.

Although the details will be omitted, the AF frame operation portion 20includes a position operation member 60 (for example, a joystick or atrackball) for moving the position of the autofocus area (the positionof the AF frame) up, down, left and right by user's manual operation, asize operation member 62 (for example, a knob) for changing the size ofthe autofocus area (the size of the AF frame) by manual operation, ashape operation member 64 (for example, a knob) for changing the shapeof the autofocus area (the shape of the AF frame) by manual operation, atracking start switch 68 for issuing an instruction to start automatictracking, and a tracking stop switch 70 for issuing an instruction tostop automatic tracking. The setting statuses of the operation members60, 62, 64, 68 and 70 are read by a CPU 38 of a main board 30 in theimaging processing unit 18.

In addition, the touch panel-including liquid crystal display(hereinafter referred to as “LCD”) is provided in the AF frame operationportion 20. The LCD 66 is configured so that setting of a mode concernedwith automatic tracking etc. can be inputted by touch operation (tap) onthe LCD 66. An image displayed on the LCD 66 can be switched suitably inaccordance with the setting contents by the CPU 38 of the imageprocessing unit 18.

Incidentally, in the case where only automatic tracking based on anautomatic tracking mode which will be described later is performed inthis embodiment, part or all of the operation members 60, 62, 64, 68 and70 of the AF frame operation portion 20 can be dispensed with. Inaddition, the LCD 66 can be also dispensed with. According to theautomatic tracking mode which will be described later, automatictracking can be performed without necessity of any operation on theoperation members 60, 62, 64, 68 and 70 and the LCD 66. The embodimentcan be preferably applied to a small-sized camera such as a handy camerain which it is difficult to spare a space for installing the AF frameoperation device. If the space is not a problem and there is noinfluence on the operability, configuration can be made in such a mannerthat part or all of the operation members 60, 62, 64, 68 and 70 or theLCD 66 are provided suitably so that the position of the AF frame can bechanged manually.

The configuration and processing contents of the image processing unit18 will be described below.

The image processing unit 18 includes a main board 30, a patternmatching process computing board 32, and a face recognition processcomputing board 34. CPUs 38, 50 and 52 are mounted in the main board 30,the pattern matching process computing board 32, and the facerecognition process computing board 34 respectively. Arithmeticprocessing is performed individually in each board. The CPUs 38, 50 and52 are connected by a bus or a control line so that exchange of data,synchronization of arithmetic processing, etc. among the CPUs 38, 50 and52 can be attained.

Processing in the image processing unit 18 is generally controlled inthe main board 30. In addition to the CPU 38 for performing arithmeticprocessing, the SCI 58, a decoder (A/D converter) 36, a super imposer42, a RAM 39 etc. are mounted in the main board 30.

The SCI 58 is an interface circuit for performing serial communicationwith the SCI 12 a of the les device 12, as described above. The SCI 58transmits the AF frame information etc. to the lens device 12. Inaddition, the SCI 58 receives information including a diaphragm value,an object distance, and a focal distance from the lens device 12.

The CPU 38 of the main board 30 performs arithmetic processing forcalculating a depth of field using the diaphragm value, the objectdistance and the focal distance acquired from the lens device 12, andcontrol processing for performing control to execute or stop automatictracking based on the calculated depth of field. The arithmeticprocessing and the control processing may be performed by any one of themain board 30, the pattern matching process computing board 32 and theface recognition process computing board 34, or by a separately providedprocessing operation board (not shown).

The decoder 36 is a circuit for converting a video signal (SDTV signal)of video images of the television camera 10 inputted to the imageprocessing unit 18 from the down converter 46 into data to which digitalprocessing can be applied in the image processing unit 18. The decoder36 performs A/D conversion processing etc. for converting an analog SDTVsignal into a video signal of digital data. The video signal of videoimages outputted from the decoder 36 is also sent to the patternmatching process computing board 32 and the face recognition processcomputing board 34 so that the video images captured by the televisioncamera 10 can be acquired as captured images each corresponding to oneframe also in the pattern matching process computing board 32 and theface recognition process computing board 34.

Incidentally, the image processing unit 18 is provided with a memoryetc. which is readable and writable by the CPU 38 and which can be usedsuitably for storage of processing data etc. In addition, informationabout the position, size and shape of the autofocus area set in the AFframe setting processing in the automatic tracking mode which will bedescribed later is stored in this memory. It is preferable that thesetting information about the position, size and shape of the autofocusarea can be changed by a predetermined operation of the AF frameoperation portion 20 in accordance with user's (cameraman's) preference.

The super imposer 42 is a circuit which combines a video signal ofcaptured video images obtained from the decoder 36 with an image signalgenerated by the CPU 38 and outputs/displays the combined video signalto/on the LCD 66. In this manner, the video images captured by thetelevision camera 10 can be displayed on the LCD 66 in the same manneras on the viewfinder 16 mounted in the camera body 14. At the same time,an image of the currently set autofocus area, a menu screen (menu image)etc. on which an input operation is allowed to be performed through thetouch panel, etc. can be displayed on the LCD 66 while superimposed onthe captured video images. Incidentally, it is a matter of course thatonly the image generated by the CPU 38 can be displayed while notsuperimposed on the captured video images.

The RAM 39 is a memory which temporarily stores data used in arithmeticprocessing of the CPU 38.

The pattern matching process computing board 32 and the face recognitionprocess computing board 34 are computing boards for individuallyperforming pattern matching and face detection/authentication process.The pattern matching process computing board 32 and the face recognitionprocess computing board 34 are provided with the CPUs 50 and 52 whichperform arithmetic processing, VRAMs 54 and 56 which temporarily storeimage data respectively, etc.

In addition, a slot (not shown) into which a face authentication datacard 74 is loaded as an external memory such as an SD (Secure Digital)card, a USB memory, etc. is provided in the image processing unit 18.When the face of a specific person is detected by face recognition,recognition data indicating the face of the specific person are storedin advance in the face authentication data card 74. When the faceauthentication data card 74 is loaded into the slot, the CPU 38 can readauthentication data required for face recognition from the faceauthentication data card 74.

Successively, control of the autofocus area performed by the imageprocessing unit 18 configured as described above will be described inconjunction with processing concerned with display and operation of theLCD 66.

FIG. 3 is a view showing an example of a screen displayed on the touchpanel-including liquid crystal display in the autofocus system accordingto the embodiment of the invention.

As shown in FIG. 3, a menu screen (menu image) including various buttons300 and 302, and an AF frame 204 indicating an autofocus area 200 (seeFIG. 2) set currently are displayed on a screen 66 a of the LCD 66 whilesuperimposed on a video image captured by the television camera 10.Images superimposed on the captured video image, like the variousbuttons 300 and 302 of the menu screen and the AF frame 204, aregenerated by the CPU 38 of the main board 30 in the image processingunit 18 shown in FIG. 1. Those images are displayed on the LCD 66 whilesuperimposed on the video image which is captured by the televisioncamera 10 and which is outputted from the decoder 36 in the superimposer 42. Incidentally, control concerned with display (displaycontents) of the LCD 66 is performed by the CPU 38.

In addition, an indicator 304 visually indicating an angle of view ofthe lens based on information acquired from the lens device 12 isprovided in the screen 66 a of the LCD.

On the other hand, the LCD 66 is provided with a touch panel. When atouch operation is performed so that the screen 66 a of the LCD 66 istouched with a finger etc., position information indicating the touchedposition (coordinates) is given to the CPU 38. In this manner, theposition and operation kind (tap, double-tap, etc.) of the touchoperation performed on the screen 66 a of the LCD 66 are detected by theCPU 38. Processing in accordance with this operation is executed by theCPU 38.

As basic operations in the screen 66 a of the LCD 66, there are anoperation for inputting an instruction assigned in advance to each ofthe buttons 300 and 302, and an operation for designating the autofocusarea (area enclosed by the AF frame 204). The former operation isperformed by tapping the position of the button 300 or 302 with a fingeretc. The latter operation for designating the autofocus area isperformed, for example, in such a manner that when a position to whichthe autofocus area is intended to be moved is tapped on the screen 66 aof the LCD 66 on which each captured video image is displayed, theautofocus area can be moved so that the position comes to the center. Inaddition, an apex or a side of the AF frame 204 indicating the contourof the autofocus area can be moved to a position to where the touchedapex or side is dragged by a dragging operation for touching the apex orside with a finger etc. and sliding the apex or side, so that theposition, size and shape of the autofocus area can be changed.

Incidentally, the position, size and shape of the autofocus area can bechanged by operations of the position operation member 60, the sizeoperation member 62 and the shape operation member 64 in the AF frameoperation portion 20.

To describe the menu screen (menu image) displayed on the screen 66 a ofthe LCD 66, a fixation mode selection button 300 indicated as “AF framefixed”, and an automatic tracking mode selection button 302 indicated as“automatic tracking” are buttons for selecting an autofocus control modein FIG. 3. When one of these buttons 300 and 302 is tapped, a desiredmode can be selected from the fixation mode and the automatic trackingmode.

The fixation mode is a mode (manual mode) in which an operatordesignates an autofocus area (the position, size and shape) by a manualoperation and an AF frame is displayed in the designated position sothat the autofocus area is fixed. This fixation mode is a mode usefulfor capturing images in a news program for which the camera is hardlymoved.

When the fixation mode selection button 300 is tapped on the screen 66 aof the LCD 66 in FIG. 3, the fixation mode is selected so that the CPU38 mounted in the main board 30 of the image processing unit 18 executesprocessing of the fixation mode.

That is, the CPU 38 determines the autofocus area based on an operationon the screen 66 a of the LCD 66 for changing the autofocus area or anoperation on an operation member (the position operation member 60, thesize operation member 62 or the shape operation member 64) for changingthe AF frame 204 provided in the AF frame operation 20 by a manualoperation, as described above. Upon determination of the autofocus area,the CPU 38 transmits AF frame information indicating contour informationof the autofocus area to the lens CPU of the lens device 12 through theSCI 58.

The automatic tracking mode is a mode for performing processing to set apredetermined object within the autofocus area, detect a presence areaof the target to be tracked in an image newly captured by the imagingunit and determine the presence area as a new autofocus area. Theautomatic tracking mode has a plurality of modes including an “objecttracking mode”, a “face detection tracking mode”, a “face recognitiontracking mode”, and a “fully automatic tracking mode”. After theautomatic tracking mode is selected on the screen 66 a of the LCD 66, adesired mode is further selected by a user from the “object trackingmode”, the “face detection tracking mode”, the “face recognitiontracking mode” and the “fully automatic tracking mode”. Incidentally,configuration may be made so that a desired mode can be selected by auser from the “object tracking mode”, the “face detection trackingmode”, the “face recognition tracking mode” and the “fully automatictracking mode” in the menu screen of the screen 66 a of the LCD 66.

The object tracking mode is a mode for tracking an arbitrary object. Atleast part of the object set as the target to be tracked is displayed tobe enclosed in the AF frame. The object tracking mode is a mode usefulfor capturing each image in horse racing broadcasting, car racingbroadcasting, or the like for tracking an object other than a person'sface. When an operator designates the autofocus area so that an image ofan arbitrary object the operator wants to set as the target to betracked is included in each of captured video images in this mode, theobject within the autofocus area enclosed by the AF frame is set as thetarget to be tracked. The image of the target to be tracked isregistered as a reference pattern and a pattern matching process fordetecting an image range coincident with the reference pattern isperformed on the sequentially obtained captured images in the CPU 50 ofthe pattern matching process computing board 32. The CPU 38 of the mainboard 30 determines the range where the reference pattern is detected asa new autofocus area, and transmits information about the autofocus areato the lens CPU of the lens device 12. Incidentally, when focus controlbased on AF is not performed in the lens device 12 while objectautomatic tracking starts (when it is not in the AF mode), aninstruction to start AF is also issued in conjunction with the start ofthe object automatic tracking.

The face detection tracking mode is a mode for tracking a face of anarbitrary person with the AF frame. A face area of the person set as thetarget to be tracked is displayed as the autofocus area to be enclosedwith the AF frame. The face detection tracking mode is a mode useful forcapturing images in a song program or the like for detecting andtracking a person's face. In this mode, first, well-known face detectionprocessing for detecting a face image of an arbitrary person from eachcaptured image is performed in the CPU 52 of the face recognitionprocess computing board 34. When an operator designates a face imagewhich is to be set as the target to be tracked from the detected faceimage, the designated face image is set as the target to be tracked.Then, face detection processing is performed on sequentially obtainedcaptured images by the CPU 52 of the face recognition process computingboard 34, and processing for identifying the face image of the target tobe tracked from the detected face images is performed by the CPU 38 ofthe main board 30. The CPU 38 of the main board 30 determines the rangeof the detected face image of the target to be tracked as a newautofocus area and transmits information about the autofocus area to thelens CPU of the lens device 12.

The face recognition tracking mode is a mode for tracking a person'sface registered preliminarily as authentication data with the AF frame.The face image of the person registered as the target to be tracked isdisplayed as the autofocus area to be enclosed with the AF frame. Theface recognition tracking mode is a mode useful for capturing images ina song program, sports broadcasting, or the like, in which each personto be imaged is determined preliminarily. In this mode, authenticationdata of the face of the person set as the target to be tracked isimported from the face authentication data card 74 loaded in the slot(not shown) shown in FIG. 1. Face detection processing is performed inthe CPU 52 of the face recognition process computing board 34 isperformed in the same manner as in the face detection tracking mode, andthe face image of the target to be tracked is detected from detectedface images by a well-known face authentication process using theauthentication data. The CPU 38 of the main board 30 determines therange of the face image detected by the face recognition process as anew autofocus area, and transmits information about the autofocus areato the lens CPU of the lens device 12.

In the fully automatic tracking mode, well-known face detectionprocessing for detecting a face image of an arbitrary person fromcaptured images is performed in the CPU 52 of the face recognitionprocess computing board 34 in the same manner as in the aforementionedface detection tracking mode. When the face image of the person isincluded in the detected face image, the face image does not have to bedesignated by an operator but can be automatically set as the target tobe tracked. When a plurality of face images are included in the capturedimage on that occasion, a face image which is to be set as the target tobe tracked is determined in accordance with the size and position of theface. On the other hand, when the face image of the person is notincluded in the captured image, automatic tracking based on theaforementioned object tracking mode is executed.

The video camera system 1 configured as described above executesautomatic tracking when the automatic tracking mode is selected. Whenautomatic tracking is performed, a depth of field is calculated based oninformation obtained from the lens device 12 and control is made toexecute or stop automatic tracking based on the depth of field. In thismanner, mistracking can be avoided even when the angle of view forcapturing an image is changed to the wide angle side by zooming of thelens device 12 at the time of execution of automatic tracking.

FIG. 4 shows an example of a screen displayed on the LCD when automatictracking is stopped. When an object as a target to be tracked becomessmall in the case where zooming is set at a wide angle as shown in FIG.4, contrast with a sufficient level cannot be obtained in the setautofocus area even if the autofocus area is set in accordance with theobject. In such a case, the depth of field is so deep that execution ofautomatic tracking is automatically stopped based on the depth of field.The autofocus area is changed to a predetermined position (for example,the center of the imaging area) so that the AF frame 204 representingthe contour of the changed autofocus area is displayed whilesuperimposed on the screen 66 a. In addition, a tracking stop mark 306visually indicating the stop of automatic tracking is displayed on thescreen 66 a. When automatic tracking is stopped, it is arbitrary thateither autofocus is performed or the lens is fixed to a previous focusposition. As will be described later, execution or stop of autofocusadjustment may be controlled based on the depth of field.

When automatic tracking is stopped, autofocus adjustment is performed onan object in the predetermined position of the imaging area (forexample, the center of the imaging area).

Successively, processing when the automatic tracking mode performed bythe image processing unit 18 is selected will be described.Incidentally, processing of the face recognition tracking mode will bedescribed as follows by way of example.

FIG. 5 is a flow chart showing a processing procedure when the automatictracking mode in the CPU of the image processing unit is selected.

When the automatic tracking mode is selected by a predeterminedoperation, first, the CPU 38 of the main board 30 performs AF framesetting processing to set an autofocus area at a predetermined initialposition. A flag (Face_flag) indicating whether face recognition isperformed or not is set to be false (step S10). In the AF frame settingprocessing, the autofocus area in an imaging range (imaging area) is setbased on information about the position, size and shape of the initiallyset autofocus area stored in the memory (not shown) of the main board30. AF frame information indicating the information (the position, sizeand shape) of the thus set autofocus area is transmitted to the lens CPUof the lens device 12 through the SCI 58. In this manner, the autofocusarea is set in a range designated by the AF frame information in the AFunit 40 of the lens device 12.

Successively, the CPU 52 of the face recognition process computing board34 imports image data of a captured image corresponding to one framefrom the decoder 36 (step S12). The CPU 38 of the main board 30 isnotified of the imported image data.

Next, the CPU 38 of the main board 30 acquires the diaphragm value, theobject distance and the focal distance from the lens device 12 (stepS14). In the step S14, the CPU 38 edits the acquired diaphragm value,object distance and focal distance as data linked to a correspondingface image, and temporarily stores the edited diaphragm value, objectdistance and focal distance in the RAM 39.

Next, the CPU 38 of the main board 30 executes arithmetic processing tocalculate the depth of field using the data including the diaphragmvalue, the object distance and the focal distance generated in the stepS14 (step S16).

In the arithmetic processing in the step S16, the depth of field iscalculated as in the following expression (1). In the expression (1), Lris the rear depth of field and Lf is the front depth of field.Depth of Field=Lr+Lf  expression (1)

The rear depth of field Lr is calculated as in expression (2). The frontdepth of field Lf is calculated as in expression (3). In the followingexpressions, the focal distance of the lens of the lens device 12 is f,the diaphragm value (f-number) is FNo, the permissible circle ofconfusion is δ, and the object distance is L.

$\begin{matrix}{{{Rear}\mspace{14mu}{Depth}\mspace{14mu}{of}\mspace{14mu}{Field}\mspace{14mu}{Lr}} = \frac{\delta \cdot {FNo} \cdot L^{2}}{f^{2} - {\delta \cdot {FNo} \cdot L}}} & {{expression}\mspace{14mu}(2)} \\{{{Front}\mspace{14mu}{Depth}\mspace{14mu}{of}\mspace{14mu}{Field}\mspace{14mu}{Lf}} = \frac{\delta \cdot {FNo} \cdot L^{2}}{f^{2} + {\delta \cdot {FNo} \cdot L}}} & {{expression}\mspace{14mu}(3)}\end{matrix}$

When a blurring amount of an image is not higher than a certain value inthe condition that the image of an object on the optical axis of thelens is formed on the imaging surface (the imaging surface of the imagesensing device), it appears as if the lens focuses in a range around thepoint where the object is brought into focus. A circle having thecertain value of the blurring amount of the image on this occasionassumed to be the diameter and the optical axis assumed to be the centeris a permissible circle of confusion. Incidentally, the diameter of thepermissible circle of confusion changes in accordance with the imagesize of the image sensing device, the performance of the camera, usageconditions, etc.

In the range where it appears as if the lens focuses, the image formingrange of the image forming surface side is referred to as the depth offocus. Incidentally, the depth d of focus can be calculated based ond=2δ×FNo.

Incidentally, the depth of field has the following properties.

(i) The depth of field is deeper as the diaphragm value is larger.

(ii) The depth of field is deeper as the focal distance is shorter.

(iii) The depth of field is deeper as the object distance is longer.

(iv) The rear depth of field is deeper than the front depth of field.

Successively to the step S16, the CPU 38 of the main board 30 comparesthe depth of field calculated in the step S16 with a predeterminedthreshold to thereby determine whether the depth of field is shallowerthan the threshold or not (step S20). Here, assume that the threshold is50% as long as the object distance. When the depth of field is shallowerthan the threshold, the processing procedure goes to step S26. When thedepth of field is not shallower than the threshold, the processingprocedure goes to step S22.

When the determination in the step S20 results in NO, the CPU 38determines that automatic tracking should be stopped, and sets automatictracking at OFF (step S22). The CPU 38 determines that the autofocusarea is moved to a set default position (for example, the center of thecaptured image), and transmits AF frame information indicatinginformation about the autofocus area to the lens CPU of the lens device12 through the SCI 58 (step S24). When the processing of the step S24 iscompleted, the procedure returns to the processing of the step S10.

When the determination in the step S20 results in YES, the CPU 38determines whether Face_flag is “false” or not (step S26). WhenFace_flag is “false”, the processing procedure goes to step S30. WhenFace_flag is “true”, the processing procedure goes to step S28.

When the determination in step S26 results in YES, the CPU 38 determineswhether the face image is detected within the captured image or not bythe face detection processing in the step S14 (step S30). When the faceimage is detected within the captured image, the processing proceduregoes to step S32. When the face image is not detected within thecaptured image, the processing procedure goes to step S36.

When the determination in the step S30 results in YES, the CPU 38 setsFace_flag at “true” (step S31). Successively to the processing of thestep S31, the CPU 38 starts automatic tracking (step S32). The CPU 38sets (updates) the range of the detected face image as a new autofocusarea, and transmits AF frame information indicating information aboutthe autofocus area to the lens CPU of the lens device 12 (step S34). Theles device 12 executes autofocus adjustment in the new autofocus areabased on the AF frame information (step S36). When the processing of thestep S36 is completed, the procedure returns to the processing of thestep S12.

When the determination in the step S26 results in NO, the CPU 38determines whether an image of a reference pattern has moved or not,that is, whether an image range in which the reference patter has beendetected is different from the currently set autofocus area or not (stepS28). Incidentally, even in the case where the size of the image of thereference pattern in the captured image has changed, determination inthe determination processing results in YES.

When the determination in the step S28 results in YES, the proceduregoes to the processing of the step S34. In the case where thedetermination in the step S28 results in NO, the procedure goes to theprocessing of the step S36.

According to the aforementioned video camera system 1, determination ismade as to whether an image of a person's face is included in a capturedimage or not in the automatic tracking mode. When determination is madethat the image of the person's face is included in the captured image,the image of the person's face is set as a target to be tracked andautomatic tracking based on face detection processing is executed. Whenthe angle of view is changed by zooming on that occasion, determinationis made as to whether execution of automatic tracking is allowed or notbased on the depth of field. When determination is made that executionof automatic tracking is not allowed, automatic tracking isautomatically stopped. When determination is made that execution ofautomatic tracking is allowed, automatic tracking is executed.

In addition, the video camera system 1 can execute automatic tracking,and control execution or stop of autofocus adjustment based on the depthof field. The video camera system 1 can control execution or stop ofautofocus adjustment in parallel with the aforementioned control ofautomatic tracking.

FIG. 6 is a flow chart showing a processing procedure when autofocusadjustment is controlled based on the depth of field.

When autofocus is executed, the CPU 38 of the main board 30 brings theobject into focus within the autofocus area set by the automatictracking mode. Successively, the CPU 38 of the main board 30 acquiresthe diaphragm value, the object distance and the focal distance from thelens device 12 (step S40).

Then, the CPU 38 of the main board 30 executes a computing process forcalculating the depth of field by using data including the diaphragmvalue, the object distance and the focal distance generated in the stepS40 (step S42).

Successively to the step S42, the CPU 38 of the main board 30 determineswhether the depth of field calculated in the step S40 is infinite or not(step S44). Here, the fact that the depth of field is infinite meansthat infinity is included in the depth of field as a result of thecomputing.

When the determination in the step S44 is made that the depth of fieldis infinite, the processing procedure goes to step S46. When thedetermination is made that the depth of field is not infinite, theprocessing procedure goes to step S48.

When the determination in the step S44 results in YES, the CPU 38 setsautofocus adjustment at OFF (step S22). The CPU 38 transmits informationindicating stop of autofocus adjustment to the AF unit 40 through theSCI 58 (step S46). When the processing of the step S46 is completed, theprocedure returns to the processing of the step S40.

When the determination in the step S44 results in NO, the CPU 38 allowsexecution of autofocus adjustment (step S48). The AF unit 40 executesautofocus adjustment in the already set autofocus area (step S48). Whenthe processing of the step S48 is completed, the procedure returns tothe processing of the step S40.

According to the aforementioned video camera system 1, when autofocusadjustment is performed, an object within a set autofocus area isbrought into focus. When the angle of view is changed by zooming on thatoccasion, determination is made as to whether execution of autofocusadjustment is allowed or not based on the depth of field. Whendetermination is made that execution of autofocus adjustment is notallowed, autofocus adjustment is automatically stopped. In addition,when determination is made that execution of autofocus adjustment isallowed, autofocus adjustment is executed.

In addition, according to the video camera system 1, the SPU 38 of themain board 30 determines whether execution of at least one of automatictracking and autofocus adjustment is allowed or not, based on the depthof field. When determination is made that the execution is not allowed,control is made to stop the execution. When control is made toautomatically turn ON/OFF automatic tracking and autofocus adjustment,mistracking can be prevented from occurring in the following case.

When there is an area in which the lens does not focus in a capturedimage and there is a moving object in the captured image and whensufficient contrast can be obtained from an image of the object withinthe autofocus area, control is made to turn ON automatic tracking andturn ON AF.

There may be a case where the lens does not focus at any position of thecaptured image and there is an object which moves in the imaging rangeof the captured image. In such a case, it is assumed that execution ofautofocus adjustment is not necessary because the depth of field isinfinite so that automatic tracking of the object is performed. In sucha case, automatic tracking is controlled to be ON and autofocusadjustment is controlled to be OFF.

In the case where there is an area in which the lens does not focus inthe captured image and the object as the target to be tracked is toosmall, sufficient contrast cannot be obtained from the image of theobject in the range of the AF area. Therefore, the accuracy of automatictracking is lowered. In such a case, automatic tracking is controlled tobe OFF and autofocus adjustment is controlled to be ON.

In the case where the lens does not focus in any position of thecaptured image and the object as the target to be tracked is too small,both automatic tracking and autofocus adjustment are controlled to beOFF.

In this specification, the autofocus system is disclosed as follows.

(1) An autofocus system including:

an imaging unit which captures an image of an object formed by anoptical system;

an autofocus portion which performs focus adjustment of the opticalsystem on an autofocus area set in the image captured by the imagingunit so that the object within the autofocus area comes into focus;

an AF area tracking processing portion which performs trackingprocessing to set a predetermined object within the autofocus area as atarget to be tracked, detect a presence area of the target to be trackedin an image newly captured by the imaging unit and determine thepresence area as a new autofocus area;

a depth-of-field computing portion which calculates a depth of fieldbased on information acquired from the optical system; and

a control portion which controls execution of the focus adjustment bythe autofocus portion and the tracking processing by the AF areatracking processing portion based on the depth of field calculated bythe depth-of-field computing portion.

(2) An autofocus system described in the paragraph (1), wherein:

the control portion makes control not to execute the tracking processingwhen the depth of field is smaller than a predetermined threshold.

(3) An automatic system described in the paragraph (1) or (2), wherein:

the control portion makes control not to execute the focus adjustmentwhen the depth of field is infinite.

(4) An autofocus system according to any of the paragraphs (1) through(3), wherein:

the depth-of-field computing portion calculates the depth of field basedon information about diaphragm value, object distance and focal distanceobtained from the optical system.

(5) An autofocus system according to any of the paragraphs (1) through(4), wherein:

the AF area tracking processing portion sets a human image within theautofocus area as a target to be tracked.

INDUSTRIAL APPLICABILITY

The autofocus system according to the invention is provided with anautomatic tracking function capable of suppressing occurrence ofmistracking when the angle of view is changed by zooming. Accordingly,the autofocus system is useful when it is applied to a digital camera,especially a compact digital camera, a camera-including cellular phone,a camera-including electronic apparatus, an endoscope imaging apparatus,or the like.

The present application is based on Japanese Patent Application No.2011-8333 filed on Jan. 18, 2011, the contents of which are incorporatedherein by reference.

EXPLANATIONS OF REFERENCE SIGNS

-   1 video camera system-   10 television camera-   12 lens device-   14 camera body-   16 view finder-   18 image processing unit-   20 AF frame operation portion-   30 main board-   40 AF unit-   32 pattern matching process computing board-   34 face recognition process computing board-   38, 50, 52 CPU-   66 liquid crystal display (LCD)

The invention claimed is:
 1. An autofocus system comprising: at leastone central processor configured to cause an imaging device to capturean image of an object formed by an optical system, and configured toperform focus adjustment of the optical system on an autofocus area setin the image captured by the imaging device so that the object withinthe autofocus area comes into focus, perform tracking processing to seta predetermined object within the autofocus area as a target to betracked, detect a presence area of the target to be tracked in an imagenewly captured by the imaging unit and determine the presence area as anew autofocus area, calculate a depth of field based on informationacquired from the optical system, and individually control whether toexecute the focus adjustment and whether to execute the trackingprocessing, based on the calculated depth of field, wherein the controlof whether to execute the tracking processing is based on a comparisonof whether the calculated depth of field is shallower than apredetermined threshold corresponding to the distance to the object, andwherein the at least one central processor controls the trackingprocessing to not be executed when the depth of field is equal to ordeeper than the predetermined threshold.
 2. The automatic system asclaimed in claim 1, wherein the at least one central processor controlsthe focus adjustment to not be executed when infinity is included in thedepth of field.
 3. The autofocus system as claimed in claim 2, whereinthe at least one central processor calculates the depth of field basedon information about diaphragm value, object distance, and focaldistance obtained from the optical system.
 4. The autofocus system asclaimed in claim 3, wherein the at least one central processor sets ahuman image within the autofocus area as a target to be tracked.
 5. Theautofocus system as claimed in claim 2, wherein the at least one centralprocessor sets a human image within the autofocus area as a target to betracked.
 6. The autofocus system as claimed in claim 1, wherein the atleast one central processor calculates the depth of field based oninformation about diaphragm value, object distance, and focal distanceobtained from the optical system.
 7. The autofocus system as claimed inclaim 6, wherein the at least one central processor sets a human imagewithin the autofocus area as a target to be tracked.
 8. The autofocussystem as claimed in claim 1, wherein the at least one central processorsets a human image within the autofocus area as a target to be tracked.